In the principle of an ink jet recording system, a liquid or a molten solid ink is jetted from nozzles, slits, porous films, etc., to perform recording on papers, cloths, films, etc. As a system of jetting an ink, there are proposed various kinds of systems such as a so-called charge control system of jetting an ink by utilizing an electrostatic attraction force, a so-called drop-on-demand system (pressure pulse system) of jetting an ink by utilizing a vibration pressure of a piezo element, a so-called thermal ink jet system of jetting an ink by utilizing a pressure generated by forming and growing bubbles by applying a heat at a high temperature etc., and by these systems, very high precise images can be obtained.
As an ink being used for such an ink jet recording system, solutions or dispersions formed by dissolving or dispersing various water-soluble dyes or pigments in a liquid medium composed of water or a water-soluble organic solvent are known and used.
For the inks described above, various improvements have been investigated.
In regard to the ink being used for an ink jet printer, following 6 points;
(1) the ink has a good quick drying property on a paper, PA1 (2) the ink gives uniform images having a high resolving power and a high density on a paper without causing blotting and fog, PA1 (3) the ink does not cause clogging of the tips of nozzles by drying and always shows a good jetting stability, PA1 (4) in a thermal ink jet system, the ink does not cause scorching on a heater or the ink does not cause a so-called heater trouble in which a material always in contact with the ink is eroded with the ink and finally a working electrode which is a part of the heater is short-circuited to make the heater unworkable, PA1 (5) the ink has a good long storage stability, and PA1 (6) even when continuous printing is carried out, the ink does not cause an image disturbance and an image defect, are investigated and for meeting these requirements, many attempts have been proposed.
Improvements of the quick drying property of the ink on papers are disclosed in JP-B-60-34992 (the term "JP-B" as used herein means an "examined published Japanese patent application"), JP-A-62-11781 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), and JP-B-62-13388 and they propose that the permeability of the ink into papers is improved by the addition of surface active agents or polyhydric alcohol derivatives.
However, in the improvements described in the foregoing patent publications, the drying property of images is improved by greatly improving the permeability of the ink into plain papers but at the same time there is a problem that the occurrence of an image blotting is increased. Also, when such an improvement is applied to a thermal ink jet system, there is a problem that scorching occurs on the heater.
On the other hand, with regard to the improvement of the quality of prints, the use of 2,2'-thiodiethanol has been variously proposed. For example, in JP-B-61-55546, it is disclosed to combine a specific dye and a solvent containing 2,2'-thiodiethanol. Also, in JP-A-1-263169, it is disclosed to combine Direct Black 168 and a specific solvent containing 2,2'-thiodiethanol.
However, when 2,2'-thiodiethanol is used, in particular, at continuous printing at a high-frequency, there are faults that images are disturbed and image defects are liable to occur, and also when 2,2'-thiodiethanol is used for a thermal ink jet system, there is a fault that a heater trouble is liable to occur.
As described above, conventionally used thermal ink jet recording inks do not satisfy all the required factors and hence the development of inks suitable for a thermal ink jet recording system has been demanded.